This application claims the priority of German Application No. 198 18 124.8, filed Apr. 23, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an arrangement for detecting the rotational speed of turbochargers on an internal-combustion engine through the use of a piezoelectric acceleration sensor.
A simple and reliable detection of the rotational turbocharger speed under all operating conditions (load and rotational speed) is the basic prerequisite for the efficient operation of a modern internal-combustion engine equipped with a turbocharger. The detected rotational speed can then be used as a control variable for automatically controlling the turbocharger and the whole characteristic diagram in the charger operation of the engine. As a result of detecting the rotational speed, it is possible to operate the turbocharger at its maximal rotational speed limit and prevent possible destruction resulting from overspeed operation. As a result, control-technical interventions are permitted in the whole engine control system.
Known arrangements for detecting the rotational turbocharger speed are based on optical and inductive processes. These processes require considerable implementing expenditures. It is known to photo-electrically or inductively scan the charger blades or additionally mounted pulse wheels on the turbocharger shaft. The scanned results are then analyzed in a high-quality electronic analyzing system coupled to receive the scanned signals.
From German Patent documents DD 257 126 and DD 269 683, it is known to mount piezoelectric acceleration sensors on the housing of rotating machines in order to thus detect the rotational speed. For analyzing the signal detected in the acceleration sensor and processed, the frequency-amplitude spectrum of the signal is determined in a signal analyzer connected on the output side, the rotational speed being determined from one of the rotational-speed-dependent resonances or on the highest occurring peaks and by a mathematical transformation. Although a very precise detection of the rotational speed can be carried out as a result, with respect to the space requirements and costs, such a high-expenditure electronic system is not suitable for a standard application in a motor vehicle.
From U.S. Pat. No. 4,864,859, it is known to mount piezoelectric acceleration sensors on housings of turbochargers. However, this known arrangement is not used for the detection of rotational speeds but rather for determining and eliminating unbalanced masses of the rotating system.
It is an object of the present invention to provide a simple arrangement for detecting turbocharger rotational speed at reasonable cost while being suitable for mass production.
According to the invention, this object is achieved by an arrangement for detecting the turbocharger rotational speed having at least one piezoelectric acceleration sensor which is fixed on the turbocharger and is constructed as a knock sensor, and having an analyzing unit with an analog filter arrangement for filtering the output signals from the acceleration sensor. The output signals of the filter arrangement, by way of a frequency-to-voltage converter in the form of an analog voltage or directly in the form of frequency signals, are provided as input signals for an electronic control unit of the internal-combustion engine or for a measuring and/or display unit.
The arrangement according to the invention has the significant advantage that the construction of the turbocharger is not important for detecting the rotational speed. In this case, the piezoelectric acceleration sensor can also be mounted subsequently in a simple manner on the turbocharger without the necessity of opening or reconfiguring this turbocharger. The rotational speed of the turbocharger can be detected in a very simple and low-cost manner. In conjunction with an achieved robust construction and a simple mounting, this arrangement is suitable for mass production at reasonable cost and for the rough operation in the motor vehicle. In this case, measurements of rotational turbocharger speeds can be carried out in a simple and low-cost manner. Since, as the result of the rotational speed detection, the turbocharger can be operated at its maximal rotational speed limit and a destruction due to overspeed hardly presents a problem, lower-cost smaller turbochargers can be used. The starting hesitation of vehicles is reduced; the gear shift level adaptation presents no problems; and a better overall efficiency of the internal-combustion engine can be achieved in every-day operation.
The piezoelectric acceleration sensor according to the invention is advantageously a commercially available knock sensor which is available in a fully developed state as a mass produced product for the automatic knock control of internal-combustion engines. It can also be used for the rotational speed detection of turbochargers at reasonable cost.
As the result of the measures described herein, advantageous further developments and improvements of the arrangement according to the invention can be achieved.
The at least one acceleration sensor is expediently arranged on the compressor housing of the turbocharger, where the vibration signals are the clearest and the best prerequisites exist for a mechanical fastening.
For synchronizing a turbocharger arrangement (such as a bi-turbo) consisting of two turbochargers on an internal-combustion engine, each of these turbochargers is expediently connected with an acceleration sensor and a corresponding analyzing circuit. In this case, devices for forming a differential rotational speed signal or a differential mode voltage by which this synchronization can be implemented are provided in the analyzing circuit or in the electronic control unit.
In the simplest case, the filter arrangement is constructed as a band pass filter.
In order to, for example, protect against excess voltages, a corresponding limiter circuit can advantageously be connected directly to the output side of the acceleration sensor.
In an implementation of the analyzing circuit which requires higher technical expenditures but is more exact, a comparator (particularly a comparator with a hysteresis) can be connected to the output side of the filter arrangement. If the electronic control unit requires an analog voltage signal as the rotational speed signal, then a low-pass filter follows the frequency-to-voltage converter provided for this purpose in order to filter out possibly remaining higher-frequency parts.
The acceleration sensor is expediently connected by way of a connection cable with an input of the electronic control unit or, for measuring purposes, with the measuring and/or display unit in order to supply measuring signals to the latter. In a first advantageous further embodiment, the analyzing circuit is integrated in the housing of the acceleration sensor, and the input of the electronic control unit or of the measuring and/or display unit is constructed as a frequency input or analog input. This depends on whether or not a frequency-to-voltage converter is provided.
In an alternative advantageous further embodiment, the analyzing circuit is integrated in a plug of the connection cable or in the connection cable itself. In this case, the input of the electronic control unit or of the measuring and/or display unit is then again constructed as a frequency input or analog input.
As a third advantageous embodiment of the invention, the analyzing circuit is arranged in the electronic control unit or in the measuring and/or display unit. In this case, the input of the electronic control unit or of the measuring and/or control unit is then constructed as an input of the analyzing circuit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.